There is known a valve timing control apparatus that controls, i.e., adjusts opening timing and closing timing of intake valves or exhaust valves, which are driven by a driven-side shaft of an internal combustion engine, by changing a rotational phase between a driving-side shaft and the driven-side shaft of the internal combustion engine. In this type of valve timing control apparatus, a pressure of hydraulic oil in advancing chambers and a pressure of hydraulic oil in retarding chambers are changed in the housing, so that the vane rotor is rotated relative to the housing to change the opening timing and closing timing of the valves.
For example, a valve timing control apparatus recited in US2012/0097122A1 includes a hydraulic pressure control valve, which controls a hydraulic pressure of hydraulic oil in advancing chambers and a hydraulic pressure of hydraulic oil in retarding chambers. In this hydraulic pressure control valve, depending on an operational position of a spool, the hydraulic oil is discharged from the retarding chambers while supplying the hydraulic oil to the advancing chambers, or the hydraulic oil is discharged from the advancing chambers while supplying the hydraulic oil to the retarding chambers. An end surface of the spool forms a part of a discharge oil passage, through which the hydraulic oil is discharged from the advancing chambers.
In the valve timing control apparatus of US2012/0097122A1, a pressure of the hydraulic oil, which is discharged from the advancing chambers, is applied to the end surface of the spool of the hydraulic pressure control valve. According to a result of a study of the inventors of the present patent application, it is found that positioning accuracy of the spool is deteriorated when the pressure of the hydraulic oil is applied to the end surface of the spool. This disadvantage of deteriorating the positioning accuracy of the spool also occurs in a case where the pressure of the hydraulic oil, which is supplied to the advancing chambers or the retarding chambers, is applied to the end surface of the spool.